Sergei Tikhanovsky was kept isolated in bare, tiny cells and tells the BBC that Belarus must free other political prisoners.
Viktor Babaryko was arrested in 2020 after challenging authoritarian leader Alexander Lukashenko at the polls.
Maria Kolesnikova, jailed for her part in mass political protests in 2020, was allowed to see her father.
Dozens of prisoners were freed unexpectedly this summer, now relatives are hoping more will follow.
The members of Tor Band have been given long jail terms after their songs became a symbol for dissent.
Eduard Babaryko was detained while running his father's presidential election campaign in 2020.
The sons of two anti-government figures are in jail because of their fathers' actions, the BBC hears.
Maria Kolesnikova is in a serious but stable condition in hospital, her allies say.
Russia is sending thousands more troops to Belarus. Is the country going to join the war in Ukraine?
